On the Seattle Weekly‘s blog, Laura Onstot lets King County’s Ron Posthuma get away with a whopper about our report on tunnel cost overruns:

…Posthuma says the Sightline report mis-characterizes at least the downtown tunnel, a project he oversaw at King County DOT. The costs blew up thanks to problems getting the stations built along the route. The tunnel itself came in under budget. “It was a double-digit percentage [under],” he said today following a viaduct replacement briefing before the King County transportation committee. Posthuma couldn’t remember the exact amount.

But this is wrong. And it’s wrong in two different ways.

First, the downtown transit tunnel project went way over budget. This is simply a matter of facts on the public record.

So let’s set the record straight. In 2007, the US Federal Transportation Administration conducted a thorough audit of selected transit projects across the country, focusing on contractor performance. FTA published several estimates of the cost overruns for the downtown Seattle transit tunnel using different points in the project’s history as a benchmark to compare to the actual cost. (See page 152 and following in the report.) Depending on which benchmark is used, the project contractors exceeded the budgets by between 17.2 percent and 63 percent.

The most relevant of these figures is 56.5 percent, both because this figure relies on the most even-handed method of accounting for inflation costs, and because it uses as a benchmark the cost estimate included in the draft environmental impact statement, rather than estimates developed later when more engineering information was available. What’s more,FTA’s analysis of cost overruns does not even include the recent retrofit to make the tunnel serviceable for Sound Transit light rail.

So, in the end, the final bill wound up being over 50 percent higher than engineers had predicted when they were designing the project.

Second, it’s wrong because it’s a classic “look-over-there!” misdirection, a sort of rhetorical sleight-of-hand. In this case, the cost overruns happened not because tunnel excavation went south, as it so often does, but in part because of unanticipated problems with making the tunnel operational. Which is exactly the point: bringing a tunnel project to completion requires a good deal more than just digging a hole in the ground.

Even when the actual tunnel digging goes okay, there are numerous related problems that can crop up. In the case of the downtown tunnel, there were problems with station positioning, worker safety, complaints from downtown property owners, and even violation of rules about materials sourcing (including a flare-up about marble from Apartheid-era South Africa). In the case of the planned downtown deep bore tunnel, it could be any number of things, some comparable to the downtown transit tunnel and some not: the close proximity to sea level; the nearby seismic fault; the costly real estate above ground; the entry and exit portals at either end; or, more likely, something that no one’s thought of yet.

Projects like these don’t tend to see cost overruns because of malfeasance or corruption, but because of predictable human traits. It sounds like a truism, but that’s only because it’s true: we don’t know what we don’t know. And what we don’t know consistently impairs our ability to forecast costs. That’s what history teaches—and that’s the lesson of Sightline’s report, Cost Overruns in Seattle-area Tunnel Projects.


Update 6/9/10: The Weeklyrepublished a version of the original blog post on their news side, but still doesn’t provide any balance to Posthuma’s inaccurate critique of Sightline’s tunnel cost report.

Update 6/11/10: The Weekly‘s Mark Fefer has an overheated blog post that is difficult to parse. It seems to accuse Sightline of hypocrisy for not critiquing light rail tunnels, despite the fact that our report actually does critique light rail tunnels.